190 



The majority of the Liverworts are found in damp and shady 

 places, pressed to the substratum ; a few are found floating in 

 fresh water. 



Family 1. Marchantiese. 



This embraces only forms with a thallus, which is more or less 

 distinctly dichotomously branched, in some, one or two rows of 

 thin leaves are situated on its under surface. On the upper 

 surface of the thallus are found large air-chambers. 



Order 1. Ricciaceae. The sporogonia are, with the excep- 

 tion of a few genera, situated singly on the surface of the thallus, 

 and consist only of a capsule without foot or stalk. They always 

 remain enclosed by the wall of the archegonium (calyptra), and open 



FIG. 197. Marcliantia polymorplia. A Female plant (nat. size) : a and b are arche- 

 goniophores in various stages of development; s cupules with gemrnas (see page 183). 

 B An archegoniophore seen from below, the short-stalked sporangia are seen placed in 

 8-10 double rows. C Male plant, with a young and an older autheridiophore. D 

 Antheridiophore halved vertically to show the antheridia (7i) ; m the aperture of the 

 pits in which they are sunk the older ones to the left, the younger to the right. 



only by its dissolution. Elaters are not developed. Some genera 

 are found floating like Duckweed. Riccia glauca grows on damp 

 clay soil. R,. fluitans and JR. natans float in stagnant waters. 



Order 2. Corsiniaceae. (Not native). Intermediate forms between the 

 preceding and the following order. In internal and external structure mainly 

 resembling the Marchantiaceae. Corsinia ; Boschia. 



Order 3. Marchantiaceae, are large, fleshy forms. The 



